Solar cells are known in the art. A solar cell may include, for example, a photoelectric transfer film made up of one or more layers located between a pair of substrates or other layers. These layers may be supported by a glass substrate. Example solar cells are disclosed in U.S. Pat. Nos. 4,510,344, 4,806,436, 6,506,622, 5,977,477, and JP 07-122764, the disclosures of which are hereby incorporated herein by reference.
Substrates in solar cells (or photovoltaic devices) are sometimes made of glass. Glass that is fairly clear in color and highly transmissive to visible light is sometimes desirable. Glass raw materials (e.g., silica sand, soda ash, dolomite, and/or limestone) typically include certain impurities such as iron, which is a colorant. The total amount of iron present is expressed herein in terms of Fe2O3 in accordance with standard practice. However, typically, not all iron is in the form of Fe2O3. Instead, iron is usually present in both the ferrous state (Fe2+; expressed herein as FeO, even though all ferrous state iron in the glass may not be in the form of FeO) and the ferric state (Fe3+). Iron in the ferrous state (Fe2+; FeO) is a blue-green colorant, while iron in the ferric state (Fe3+) is a yellow-green colorant. The blue-green colorant of ferrous iron (Fe2+; FeO) is of particular concern when seeking to achieve a fairly clear or neutral colored glass, since as a strong colorant it introduces significant color into the glass. While iron in the ferric state (Fe3+) is also a colorant, it is of less concern when seeking to achieve a glass fairly clear in color since iron in the ferric state tends to be weaker as a colorant than its ferrous state counterpart.
It has been found that the use of a low-iron highly transparent (optionally patterned) glass is advantageous for solar cell applications. The use of the low-iron composition in combination with the patterned surface(s) of the glass substrate(s) has been found to be advantageous with respect to optical properties, thereby leading to increased solar efficiency of a solar cell.
U.S. Patent Document Nos. 2004/0209757, 2005/0188725 and U.S. Pat. No. 6,949,484 disclose clear glass compositions, and are hereby incorporated herein by reference. Unfortunately, the glasses of these patent documents are lacking in terms of total solar (TS) transmission. In particular, the glasses of these patent documents have undesirably low ultraviolet (UV) transmission characteristics which leads to low total solar (TS) transmission characteristics. For example, in 2004/0209757 Examples 1-11 have UV transmission (% UV) of no more than about 77% which leads to corresponding undesirably low total solar transmission (% TS) values. As another example, in 2005/0188725 Examples 1-5 have % FeO content and glass redox values which indicate that these glasses too would have less than desirable % UV and % TS characteristics. As yet another example, in U.S. Pat. No. 6,949,484 Examples 1-11 have rather low UV transmission (% UV) of no more than about 77% which leads to corresponding undesirably low total solar (% TS) values.
It will be appreciated that low % UV and % TS values are undesirable for glass substrates of solar cell type photovoltaic devices, especially for glass substrates on the light incident side of such devices. This is because in solar cell applications it is generally desirable for the glass substrate on the light incident side to allow through it as much radiation as possible (UV, IR and visible) so that the photoelectric transfer film of the solar cell can convert the radiation to as much current as possible. The less radiation allowed to pass through the glass substrate, the less current generated in the photovoltaic device.
In certain example embodiments of this invention, a glass is made so as to be highly transmissive to visible light, to be fairly clear or neutral in color, and to realize higher % IR and/or % UV, and thus higher % TS, characteristics than those discussed above in connection with U.S. Patent Document Nos. 2004/0209757, 2005/0188725 and U.S. Pat. No. 6,949,484. In certain example embodiments of this invention, a soda-lime-silica based glass is based on low iron raw materials, has a low amount of total iron, and is extremely oxidized so as to have no or very little ferrous (Fe2+; FeO). This permits the glass to have a higher % UV transmission, and thus a higher % TS transmission, which are beneficial in solar cell applications. The glass substrate may be patterned, or not patterned, in different example embodiments of this invention.
In certain example embodiments, the glass substrate may have fairly clear color that may be slightly yellowish (a positive b* value is indicative of yellowish color). For example, in certain example embodiments, the patterned glass substrate may be characterized by a visible transmission of at least about 91%, a total solar/energy value of at least about 90%, more preferably at least about 91%, a transmissive a* color value of from −1.0 to +1.0 (more preferably from −0.5 to +0.5, and most preferably from −0.2 to 0), and a transmissive b* color value of from 0 to +1.5 (more preferably from +0.1 to +1.0, and most preferably from +0.2 to +0.6). These properties may be realized at an example non-limiting reference glass thickness of about 4 mm.
In certain example embodiments of this invention, there is provided a solar cell comprising: a glass substrate; first and second conductive layers with at least a photoelectric film provided therebetween; wherein the glass substrate is of a composition comprising:
Ingredientwt. %SiO267-75%Na2O10-20%CaO 5-15%total iron (expressed as Fe2O3)0.001 to 0.05%% FeO<=0.0038glass redox<=0.12antimony oxide0 to less than 0.01%cerium oxide0 to 0.2%, andwherein the glass substrate has visible transmission of at least 91%, a transmissive a* color value of −1.0 to +1.0, a transmissive b* color value of from 0 to +1.5, % TS of at least 90%, and a UV transmission of at least 80%.
In other example embodiments of this invention, there is provided a solar cell comprising: a glass substrate; at least a first conductive layers and a photoelectric film; wherein the glass substrate is of a composition comprising or consisting essentially of:
Ingredientwt. %SiO267-75%Na2O10-20%CaO 5-15%% FeO<=0.0038glass redox<=0.12, andwherein the glass substrate has visible transmission of at least 91%, a % TS of at least 90%, and a UV transmission of at least 80%.
In other example embodiments of this invention, there is provided a glass composition comprising or consisting essentially of:
Ingredientwt. %SiO267-75%Na2O10-20%CaO 5-15%total iron (expressed as Fe2O3)0.001 to 0.05%% FeO<=0.0038glass redox<=0.12antimony oxide0 to less than 0.01%wherein the glass at a reference thickness of about 4 mm has a visible transmission of at least 91%, a transmissive a* color value of −1.0 to +1.0, a transmissive b* color value of from 0 to +1.5, % TS of at least 90%, and a UV transmission of at least 80%.
In other example embodiments of this invention, there is provided a method of making a glass composition, the method comprising providing a glass batch that is processed so as to result in a glass comprising:
Ingredientwt. %SiO267-75%Na2O10-20%CaO 5-15%total iron (expressed as Fe2O3)0.001 to 0.05%% FeO<=0.0038glass redox<=0.12wherein the glass batch has a batch redox of from +12 to +30 during the processing of manufacturing the glass so that the resulting glass is highly oxidized and has a glass redox of no more than 0.12.